This application is based on U.S. patent application Ser. No. 11-18984 (1999) filed Jan. 27, 1999 in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an ink jet print head in which ink paths for ejecting ink droplets are formed by joining together a grooved top plate and a heater board by a press member.
2. Description of the Prior Art
An ink jet printing system is recognized as a very effective printing system because it performs non-impact printing that produces virtually no noise during printing, because it is capable of high speed printing and because it requires no special fixing of a printed image on plain paper as a recording medium.
FIG. 14 is a schematic perspective view showing an essential portion of a conventional ink jet print head disclosed in Japanese Patent Application Laid-Open No. 3-101957. FIG. 15 is a cross section taken along the line Yxe2x80x94Y of FIG. 14.
In FIGS. 14 and 15, reference number 112 represents a heater board having a plurality of electrothermal transducers (not shown) as a heat source. A grooved top plate 113 has integrally formed therein a plurality of ink orifices 101, grooved ink paths 105 communicating with the ink orifices 101, wall portions 106 forming ink paths walls, and a recessed portion as a common liquid chamber 107 for supplying ink to the ink paths 105. Denoted 111 is a base plate to support components. Designated 114 is a spring member that joins together the heater board 112 and the grooved top plate 113 by a pressing force to form the ink paths 105.
The spring member 114 has a bent end portion 114A formed at its free end and presses it against a flat upper surface 113B of the top plate 113 to engage the top plate 113 with the heater board 112, with a pressing force of the spring member acting through a line contact. It has been a conventional practice to form the spring member 114 with the rigid bent end portion 114A and press the bent end portion 114A against the upper surface 113B of the top plate 113 to join the two membersxe2x80x94the top plate 113 and the heater board 112xe2x80x94with the pressing force.
The ink jet printers of recent years have undergone price and size reductions and there is a corresponding increase in demand for a simplified structure of the ink jet print head. In a print head structure in which the top plate 113 is joined to the heater board 112 fixedly mounted on the base plate 111, the size of the print head is basically determined by the size of the base plate 111 and thus it is effective in reducing the size of the head to eliminate, or reduce the size of, the base plate 111. The structure with the base plate 111 eliminated or reduced in size, however, loses a heat dissipating function, one of the functions of the base plate 111, and thus requires some measures to suppress a temperature rise in the print head.
The official gazette of Japanese Patent Application Laid-Open No. 10-71715 discloses a technology in which the base plate is either eliminated or reduced in size to achieve a size reduction of the print head and also suppress a temperature rise in the print head.
FIG. 16 is an exploded perspective view of a conventional ink jet print head disclosed in the Japanese Patent Application Laid-Open No. 10-71715.
The print head of FIG. 16 has an orifice plate 202 formed with a plurality of ink orifices 201, a grooved top plate 200 having ink paths 203 and a common liquid chamber 204 integrally formed therein, a heater board 210 connected with a printed circuit board 205, and a spring press member 220. Instead of pressing the upper surface of the top plate 200 as in the preceding conventional art, this print head has the underside of the heater board 210 pressed by the spring press member 220 to bind the grooved top plate 200 and the heater board 210 together. The spring press member 220 is supported like a cantilever on a top plate mount (not shown) integrally formed with the grooved top plate 200.
In this print head, as shown in FIG. 17, the spring press member 220 presses the back of the heater board 210 at a position close to where electrothermal transducers 211 are installed, at a contact angle xcex8 with a pressing force acting through a line contact, to ensure an intimate contact between the top plate 200 and the heater board 210. Further, in this print head, the spring press member 220 is made of a good thermal conductive material to release heat generated by the electrothermal transducers 211. The spring press member 220 is assigned a heat dissipating function of the base plate 111 of the prior art shown in FIG. 14.
(1) In the conventional technology, however, because the spring press member 220 presses, at a contact angle xcex8, a vicinity of the front edge of the heater board 210 close to where the electrothermal transducers 211 are installed as shown in FIG. 17, moments of force B and C as shown in FIG. 17 are generated. Hence, with this conventional technology the rear end of the heater board 210 tends to float from the grooved top plate 200. This makes the contact between them unstable.
(2) The grooved top plate 200 is made of a molding resin material and can easily produce warping and bending. As described earlier, the spring press member 220 is supported on the top plate mount formed integral with the grooved top plate 200, so that when the top plate 200 is warped or bent, the spring press member 220 is shifted from its normal support position and support angle. As a result, the position and angle of the pressing portion of the spring press member 220 are deviated.
Because the heater board 210 of the conventional technology is pressed by a pressing force acting through a line contact despite the fact that the spring press member 220 has variations in its position and attitude caused by warping and bending of the top plate 200, the pressing force acting through a line contact is directly affected by the variations in position and attitude of the spring press member 220 and is likely to fluctuate or be unevenly distributed. The conventional technology therefore has a problem of not being able to bind the top plate 200 and the heater board 210 together with a uniform contact pressure with respect to the arrangement direction of ink paths 8.
The present invention has been accomplished to solve the problem described above. It is therefore a primary object of the invention to provide an ink jet print head having a base plate eliminated or reduced in size in which the grooved top plate and the heater board are engaged together with a uniform pressure over their entire contact surface to securely hold them in close contact with each other.
It is another object of the invention to provide an ink jet print head capable of dissipating heat with an improved efficiency.
According to a first aspect of the present invention, the ink jet print head comprises: a grooved top plate having a plurality of groove-like ink paths, a common liquid chamber for supplying ink to the plurality of ink paths and a plurality of orifices for ejecting ink; a heater board having a plurality of heat generating elements for generating an ink ejection pressure arranged at positions on a front surface thereof corresponding to the plurality of ink paths; and a press member for pressing and joining together the grooved top plate and the heater board; wherein the press member presses against a back of the heater board at the vicinity of a joint gravity center of the heater board and the grooved top plate.
With this invention, because the press member presses against the back of the heater board at the vicinity of the joint gravity center of the heater board and the grooved top plate to bring the heater board and the grooved top plate into intimate contact with each other, it is possible to engage the heater board and the grooved top plate with a uniform pressure over their entire contact surface. This in turn enables the heater board and the grooved top plate to be intimately joined together for a long period of time. It is therefore possible to produce a stable ink ejection pressure in each ink path, thereby realizing a high quality printing.
In this invention, the plurality of projections formed on the press member are pressed against the back of the heater board at a plurality of points that are almost equal in position to the joint gravity center with respect to the longitudinal direction of the ink paths. This enables the heater board and the grooved top plate to be joined together with a uniform pressure over their entire contact surface even when the grooved top plate has warping or bending.
According to a second aspect of the present invention, the ink jet print head comprises: a grooved top plate having a plurality of groove-like ink paths, a common liquid chamber for supplying ink to the plurality of ink paths and a plurality of orifices for ejecting ink; a heater board having a plurality of heat generating elements for generating an ink ejection pressure arranged at positions on a front surface thereof corresponding to the plurality of ink paths; a press member for pressing and joining together the grooved top plate and the heater board; and a heat dissipating member arranged on a back of the heater board; wherein the press member presses against a back of the heat dissipating member at a position on the heat dissipating member corresponding to the vicinity of a joint gravity center of the heater board and the grooved top plate.
Because the heat dissipating member with a large heat conductivity is placed on the back of the heater board, the heat dissipating performance of the heater board can be improved. Further, because the heat dissipating member is arranged on the back of the heater board, the press member presses the heater board through the heat dissipating member. The pressing position on the heat dissipating member is the joint gravity center of the grooved top plate and the heater board, as in the first aspect of the invention. Therefore, this second aspect of the invention also produces the similar effects to those of the first aspect of the invention, such as the ability to join the heater board and the grooved top plate together with a uniform pressure over their entire contact surface.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.